This invention relates to novel liquid crystal compounds having a large negative dielectric anisotropy and useful as a component of liquid crystal compositions, and also to a liquid crystal composition containing the same.
Display elements having liquid crystals applied therein utilize the optical anisotropy and dielectric anisotropy of liquid crystal substances, and they are classified into various modes such as those of TN type (twisted nematic type), DS type (dynamic scattering type), guest-host type, DAP type, etc. depending on their display modes, and there vary the properties of liquid crystal substances suitable to use for the respective modes. Liquid crystals for the above uses are required to have common properties that they are stable to moisture, air, heat, light, etc., and those have been desired which exhibit liquid-crystalline phases within a temperature range as broad as possible, centered around room temperature.
At present, there is no compound which alone satisfies such conditions; hence liquid crystal compositions obtained by mixing several kinds of liquid crystal compounds or these compounds together with non-liquid-crystalline compounds have been used.
Recently, guest-host type liquid crystal display elements in one of color liquid crystal display modes have come to be particularly noted. The elements use a mixture of liquid crystals with a dyestuff, and liquid crystal materials having a negative dielectric anisotropy are used in positive type guest-host mode display elements. Thus, as a component constituting the liquid crystal composition, a liquid crystal compound has been required which has a negative value of dielectric anisotropy the absolute value of which is as large as possible, and also has a low viscosity and a superior compatibility.